An Yb:KYW femtosecond regenerative amplifier with combination of two gain spectra from a single thin disk is presented. The amplifier generated an average power of 10 W after compression at a repetition rate of 20 kHz resulting in a pulse energy of 500 µJ. A bandwidth of 18.6 nm at â’20 dB allowed a compression to nearly Fourier-limited pulses with a duration of 185 fs resulting in a peak power of 2.7 GW.